Difference Between Covalent Molecular and Covalent Network

Main Difference – Covalent Molecular vs Covalent Network

Covalent bonds are a type of chemical bonds. A covalent bond is formed when two atoms share their unpaired electrons. Covalent bonds form between nonmetal atoms. These atoms may belong to the same element or different elements. The electron pair that is being shared between the atoms is called a bond pair. Depending on the electronegativity of the atoms that participate in this sharing, the covalent bond may either polar or nonpolar. The term covalent molecular is used to explain molecules that are formed by covalent bonding. A covalent network is a compound composed of a continuous network throughout the material in which the atoms are bonded to each other via covalent bonds. This is the main difference between covalent molecular and covalent network.

Key Areas Covered

1. What is Covalent Molecular
      – Definition, Properties
2. What is Covalent Network
      – Definition, Properties
3. What is the Difference Between Covalent Molecular and Covalent Network
      – Comparison of Key Differences

Key Terms: Bond Pair, Covalent Bond, Covalent Molecular, Covalent Network, Electron, Electronegativity, Nonmetal Atoms, Nonpolar, Polar

Difference Between Covalent Molecular and Covalent Network - Comparison Summary

What is Covalent Molecular

The term covalent molecular structure describes molecules having covalent bonds. A molecule is a group of atoms bonded together through chemical bonds. When these bonds are covalent bonds, these molecules are known as covalent molecular compounds. These covalent molecular structures can be either polar compounds or nonpolar compounds depending on the electronegativity of the atoms that are involved in bond formation. A covalent bond is formed between atoms that have similar or nearly similar electronegativity values. But if the difference between the electronegativity values of the atoms is considerably high (0.3 – 1.4), then the compound is a polar covalent compound. If the difference is less (0.0 – 0.3), then the compound is nonpolar.

Difference Between Covalent Molecular and Covalent Network

Figure 1: Methane is a Covalent Molecular Compound

Most covalent molecular structures have low melting and boiling points. This is because the intermolecular forces between covalent molecules require a lower amount of energy to separate from each other. Covalent molecular compounds usually have a low enthalpy of fusion and vaporization due to the same reason. The enthalpy of fusion is the amount of energy that is required to melt a solid substance. The enthalpy of vaporization is the amount of energy required to vaporize a liquid. These terms are used to describe the energy exchange in phase transition of matter. Since the attraction forces between covalent molecules are not strong, the amount of energy required for these phase transitions is low.

Since covalent bonds are flexible, covalent molecular compounds are soft and relatively flexible. Many covalent molecular compounds do not dissolve in water. But there are exceptions as well. However, when a covalent compound is dissolved in water, the solution cannot conduct electricity. This is because covalent molecular compounds cannot form ions when dissolved in water. They exist in the form of molecules surrounded by water molecules.

What is Covalent Network

Covalent network structures are compounds where atoms are bonded by covalent bonds in a continuous network extending throughout the material. There are no individual molecules in a covalent network compound. Therefore, the whole substance is considered as a macromolecule.

These compounds have higher melting and boiling points since covalent network structures are highly stable. They are insoluble in water. Hardness is very high due to the presence of strong covalent bonds between atoms throughout the network structure. Unlike in covalent molecular structures, the strong covalent bonds here should be broken in order to melt the substance. Therefore, these structures exhibit a higher melting point.  

Figure 2: Graphite and Diamond Structures

Figure 2: Graphite and Diamond Structures

The most common examples of covalent network structures are graphite, diamond, quartz, fullerene, etc. In graphite, one carbon atom is always bonded to three other carbon atoms via covalent bonds. Therefore, graphite has a planar structure. But there are weak Van der Waal forces between these planar structures. This gives graphite a complex structure. In diamond, one carbon atom is always bonded to four other carbon atoms; thus, diamond gets a giant covalent structure.

Difference Between Covalent Molecular and Covalent Network

Definition

Covalent Molecular: Covalent molecular structure refers to molecules having covalent bonds.

Covalent Network: Covalent network structures are compounds whose atoms are bonded by covalent bonds in a continuous network extending throughout the material.

Melting Point and Boiling Point

Covalent Molecular: Covalent molecular compounds have low melting and boiling points.

Covalent Network: Covalent network compounds have very high melting and boiling points.

Intermolecular Interactions

Covalent Molecular: There are weak Van der Waal forces between covalent molecular structures in a covalent compound.

Covalent Network: There are only covalent bonds in a covalent network structure.

Hardness

Covalent Molecular: Covalent molecular compounds are soft and flexible.

Covalent Network: Covalent network compounds are very hard.

Conclusion

Covalent molecular structures are compounds containing molecules with covalent bonds. Covalent network structures are compounds composed of a network structure with covalent bonds between atoms throughout the material. This is the main difference between covalent molecular and covalent network.

References:

1. Helmenstine, Anne Marie. “Learn the Properties and Characteristic of Covalent Compounds.” ThoughtCo, Available here.
2. “Covalent Network Solids.” Chemistry LibreTexts, Libretexts, 31 Jan. 2017, Available here.
3. Horrocks, Mathew. Molecules and networks. 4collge. Available here.

Image Courtesy:

1. “Diamond and graphite2″ By Diamond_and_graphite.jpg: User:Itubderivative work: Materialscientist (talk) – Diamond_and_graphite.jpgFile:Graphite-tn19a.jpg (CC BY-SA 3.0) via Commons Wikimedia

About the Author: Madhusha

Madhusha is a BSc (Hons) graduate in the field of Biological Sciences and is currently pursuing for her Masters in Industrial and Environmental Chemistry. Her interest areas for writing and research include Biochemistry and Environmental Chemistry.

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